1. Field of the Invention
The present invention relates to hinge assemblies, and particularly to a hinge assembly for foldable electronic devices such as mobile telephones, electronic notebooks, and so on.
2. Description of Prior Art
With the development of the technologies of wireless communication and information processing, portable electronic devices such as mobile telephones and electronic notebooks are now in widespread use. These electronic devices enable consumers to enjoy the convenience of high technology services anytime and anywhere. Foldable electronic devices are particularly favored by consumers for their convenience.
Generally, foldable electronic devices have most of the electronics in one housing, called the body. The other housing, called the cover, normally contains fewer electronic components than the body. Other foldable electronic devices have all the electronics in the body, with the cover containing no electronics. Various types of hinge assemblies are used to join a body and a cover of a foldable electronic device, so that the cover can unfold up from and fold down upon the body.
U.S. Pat. No. 6,175,990 issued on Jan. 23, 2001 provides a hinge assembly used in a small-size foldable electronic device such as a portable telephone, a portable computer, an electronic notebook or the like. As represented in FIG. 7, the hinge assembly includes a shaft 100 provided with a discoid head 102 on a first end portion thereof, a fixing member 200, a fixed cam 300, a rotary sliding cam 400, and a compression spring 502. An opposite second end portion of the shaft 100 is passed through the fixed cam 300, the rotary sliding cam 400, the compression spring 502 and the fixing member 200 in that order, thereby integrating the hinge assembly into a complete unit.
The fixed cam 300 abuts the head 102 of the shaft 100, and is rotatable relative to the shaft 100. A pair of opposite recessed cam portions 302 is defined on an end face of the fixed cam 300. A pair of opposite projection portions 402 is formed on an end face of the rotary sliding cam 400, corresponding to the cam portions 302. With the engagement of the cam portions 302 and the projection portions 402, the fixed cam 300 and the rotary sliding cam 400 are axially movable relative to each other and rotatable relative to each other. The rotary sliding cam 400 is axially movable relative to the shaft 100, and rotatable with the shaft 100. The fixing member 200 is secured around the second end portion of the shaft 100. The compression spring 502 is elastically engaged around the shaft 100 between the rotary sliding cam 400 and the fixing member 200, and continually presses the rotary sliding cam 400 against the fixed cam 300.
When the projection portions 402 of the rotary sliding cam 400 are engaged with the cam portions 302 of the fixed cam 300, the foldable electronic device is in a closed position. When the foldable electronic device is opened, the projection portions 402 move out from engagement with the cam portions 302 onto coplanar end faces of the fixed cam 300. Once the foldable electronic device is opened to an angle of about 160°, the projection portions 402 snappingly engage into the corresponding cam portions 302 and are locked therein. However, during the process of the foldable electronic device being opened, a body and a cover of the foldable electronic device are directly subjected to force produced by the fixed cam 300, the rotary sliding cam 400 and the compression spring 500. This force is liable to cause damage to the body and the cover.
In view of the above-described shortcomings, a new, safer and more durable hinge assembly is desired.